Trust me, that was not a GM-sponsored publicity stunt.
A good buddy of mine is very high up in the GM public relations hierarchy. There's no way he'd buy into that kind of a scheme. (And he's a lifelong hard-core fast car guy.)
In these days of hugely influential (good or bad) social media, car companies are no longer doing off-the-books illegal driving stunts to gain publicity. Just one bad thing happening, or even the suggestion of improper corporate citizenship, and the social media trolls (as well as conventional media) would inundate.
If GM had wanted to stage a "Corvette engineers get stopped by Bowling Green PD" sort of thing, it would've been cleared with everyone involved, done on a closed road with safety equipment and personnel in place, etc.